The present invention relates to a flat-membrane separating arrangement which can be used in such processes as ultrafiltration, reverse osmosis, and the like, for separating dissolved and also partially suspended substances from pure or colloidal solutions.
Flat-membrane separating arrangements of the above mentioned general type are known in the art. This arrangement has in general different means which produce a liquid flow on the upper surfaces of the membranes, and wherein the process-blocking cover layers of the membranes are prevented and excessive concentrations in the vicinity of the membrane are continuously decreased. In many known flat-membrane separating arrangements, the depolarization liquid is passed through differently shaped narrow gaps. Another solution is also known, which eliminates the disadvantages of the gap depolarization and wherein circulating membrane elements, such as rotatable disks, or partially rotatable disks, or a completely rotatable arrangement, are taken into consideration. Further solutions include one-chamber experimental cells in which stirrers, vibramixers and tangentially arranged nozzles are used for spin generation. With acceptance of the spin depolarization these elements cannot, however, lead to the known industrially used multi-chamber separating arrangements. The ultrafiltration arrangement is a first solution in which the features of the spin cell are combined in a separating arrangement with several superposed chambers. The press-like assembled chambers are brought into a pressure container which is charged with the aid of pressure air and/or rotary pump with the solution to be separated, so that the nozzle-like inlet passages of the spin ring, arranged in the plate packet, do not need separate supply conduits. This solution is disadvantageous in that it transmits the principle of the spin cell so that the spin flow is carried out by nozzles. As a result of this, considerable loading takes place in the vicinity of the nozzles and leads to destruction of the separation-active layer of the membrane and thereby to premature stoppage of the operation. Further disadvantages of this solution is that the spin depolarization provides considerable advantages as compared with other principles only when certain conditions are completely satisfied, which can be realized with one or several nozzles in each chamber only to a limited extent. This is disclosed in the East German patent application No. DD-WP 114,205. During the generation of a spin flow with the aid of nozzles, an unfavorable cross-sectional ratio of the nozzle opening and the spinning chamber takes place, so that a considerably greater speed is produced in the nozzle as compared with the circumferential component at the outer edge of the spin chamber. Thereby high friction losses and further considerable energy losses take place so that at the location of the flow unification in the vicinity of the nozzle the speed difference is considerably nullified. A further considerable reduction of the circumferential component is also caused because the spin flow requires a meridian component which can occur at the outer edge of the spin chamber with the tangential cross section expansion, so that with increased distance from the nozzle it respectively reduces and thereby the edge conditions of the spin flow are worsened. These disadvantages as a whole are not eliminated in the arrangement including several nozzles in each chamber, inasmuch as the speed differences at the outer edge can be reduced, however at the same cross section the circulating quantity is reduced proportionally to a reduced diameter of the nozzle and the solid-material-loading capacity of the separating arrangement is still considerably reduced.